The proposed research is intended to elucidate a variety of problems within the broad field of Thyroidology. The over-all interest is to clarify multiple aspects of thyroid hormone economy in normal animals and humans and in patients with thyroid dysfunction. Among the major topics to be studied are: 1. Extrathyroid Factors that Regulate Thyroid Function; 2. Biochemical Studies of Thyroregulatory Mechanism; 3. Responses of the Normal and Abnormal Human Thyroid to Iodine; 4. Transport and Metabolism of Thyroid Hormones; 5. Studies of the Cellular and Subcellular Effects of Thyroid Hormones; 6. Miscellaneous Studies Related to Thyroid Disease. Within each of these broad categories, several individual studies are proposed.